In recent years, there has been a strong trend in the cosmetics market in the direction of the most natural products possible. In order to be able to satisfy this, it is necessary to be able to offer high-performance emulsifiers based on renewable raw materials.
Customary emulsifiers in cosmetics often contain polyethylene glycol groups (PEG) as hydrophilic groups; the compounds including PEG groups can be prepared by polymerization of ethylene oxide obtained by a petrochemical route. Since all of the raw materials used in formulations that are as natural as possible should originate from renewable sources, PEG-containing emulsifiers are undesired in such formulations.
Polyglycerol esters are a preferred PEG-free alternative to cosmetic emulsifiers based on renewable raw materials.
The use of polyglycerol esters in cosmetics as emulsifier is well-known technology. EP-B-0 835 862 describes polyglycerol partial esters which are obtainable by esterifying a polyglycerol mixture with a degree of esterification of the polyglycerol between 30 and 75% and saturated or unsaturated, linear or branched fatty acids having 12 to 22 carbon atoms and dimer fatty acids with an average functionality of from 2 to 2.4. The polyglycerol partial esters described in EP-B-0 835 862 have the advantage that in particular the freeze-stability of these emulsions is very good. However, the emulsions are still relatively viscous and are water-in-oil (W/O) emulsions, for which reason these polyglycerol partial esters are primarily suitable for producing rich lotions and creams.
A further alternative for PEG-free natural emulsifiers is also citric acid esters. The use of esters of citric acid in cosmetics, as an emulsifier or a solubilizer, has been known for a long time; thus, for example, the 01W emulsifier glyceryl stearate citrate, (2-hydroxy-1,2,3-propanetricarboxylic acid 1,2,3-propanetriol monooctadecanoate, INCI Glyceryl Stearate Citrate, CAS 39175-72-9), the citric acid ester of glyceryl stearate, is commercially available, inter alia, under the name AXOL C 62 from Evonik Goldschmidt
WO2006034992 and WO2008092676 describe, for example, a cosmetic oil-in-water (O/W) emulsion comprising glyceryl stearate citrate in conjunction with further emulsifiers.
WO2004112731 describes an O/W emulsifier comprising glyceryl oleate citrate and a viscosity modifier.
A disadvantage of using citric acid esters is their high hydrolysis sensitivity, which usually limits the scope of use of these emulsifiers to a pH range from 5.5 to 8. This is particularly disadvantageous for developing cosmetic formulations that are as natural as possible which are intended, for example, to correspond to Ecocert. For cosmetic products which are to correspond to Ecocert requirements, generally only organic acids such as benzoic acid or sorbic acid can be used for preservation; these, in turn, require a pH of the emulsions of 4-5. Consequently, customary citric acid esters cannot be used in such formulations.
Simple polyglycerol esters, such as, for example, polyglycerol-3 distearate, are generally characterized by a limited formulation flexibility which is exhibited, for example, in emulsion instabilities in critical emulsion systems.
Mixed esters of polyglycerol and methylglucose and stearic acid, such as, for example, polyglyceryl-3 methylglucose distearate have an excellent stabilization potential and a broad spectrum of use. However, the methyl groups present in these products are based on the raw material methanol, and are therefore in part also of petrochemical origin.
In principle, it is also possible to use sorbitan esters or sucrose esters as O/W emulsifiers. A customary combination is, for example, sorbitan stearate and sucrose cocoate. However, these combinations are also generally characterized by a limited emulsion stabilization and low formulation flexibility.